Heretofore, nickel-cadmium batteries were particularly the main current as a secondary cell for backing up memories in AV-information equipments such as personal computers, VTR and the like or a power source for driving them. Recently, non-aqueous electrolyte secondary cells are considerably noticed instead of the nickel-cadmium battery because they are high in the voltage and have a high energy density and develop an excellent self-discharge characteristic, and hence various developments are attempted and a part thereof is commercialized. For example, a greater number of note-type personal computers, mobile phones and so on are driven by such a non-aqueous electrolyte secondary cell.
In the non-aqueous electrolyte secondary cell, since carbon is frequently used as a material forming a negative electrode, various organic solvents are used as an electrolyte for the purpose of reducing a risk when lithium is formed on the surface and rendering a driving voltage into a higher level. Also, an alkali metal or the like (particularly, lithium metal or lithium alloy) is used as a negative electrode in the non-aqueous electrolyte secondary cell for a camera, an aprotic organic solvent such as ester type organic solvent or the like is usually used as an electrolyte.
However, the non-aqueous electrolyte secondary cells have the following problems as to the safety though the performance is high. Firstly, when the alkali metal (particularly lithium metal, lithium alloy or the like) is used as the negative electrode in the non-aqueous electrolyte secondary cell, since the alkali metal is very high in the activity to water content, there is a problem that if water is penetrated into the cell due to incomplete sealing thereof or the like, risks of generating hydrogen by reacting the material of the negative electrode with water, ignition and the like become high. Also, since the lithium metal is low in the melting point (about 170° C.), there is a problem that if a large current violently flows in short-circuiting or the like, there is caused a very risky state that the cell abnormally generates heat to cause the fusion of the cell or the like. Further, there is a problem that the electrolyte based on the above organic solvent is vaporized or decomposed accompanied with the heat generation of the cell to generate a gas or the explosion-ignition of the cell are caused by the generated gas.
In order to solve the above problems, there is proposed a technique that a cylindrical battery is provided with such a mechanism that when a temperature rises in the short-circuiting and overcharging of the cylindrical battery to increase a pressure inside the battery, a safety valve is actuated and at the same time a terminal of the electrode is broken to control the flowing of excess current of not less than a given quantity into the battery (Nikkan Kogyo Shinbun-sha, “Electron Technology”, 1997, vol. 39, No. 9). However, it is not reliable that the above mechanism is always and normally operated. If the mechanism is not normally operated, there is remained a problem that the heat generation due to the excess current becomes large to fear a risky state of ignition or the like.
Furthermore, the conventional non-aqueous electrolyte secondary cell has a problem in view of long-running stability of the cell and the like that when an ester-based electrolyte or the like is used as a non-aqueous electrolyte, a lithium ion source or the like such as LiPF6 or the like as a support salt is decomposed into LiF and PF5 with the lapse of time to generate PF5 gas or the generated PF5 gas is further reacted with water or the like to generate hydrogen fluoride gas, and the corrosion of the electrode and the like by these gases proceeds or the electrode and the electrolyte are reacted accompanied with the discharge-recharge cycling of the cell to decompose the electrolyte.
Moreover, a lithium secondary cell conducting the discharge-recharge cycle by oxidation-reduction of lithium metal has hitherto been utilized as a non-aqueous electrolyte cell having high output and energy density. In such a lithium secondary cell, when lithium metal is used as an active substance for negative electrode, a highest theoretical capacity is obtained, so that various studies are actively conducted in various fields requiring miniaturization and weight reduction of the cell.
In the secondary cell containing the lithium metal as an active substance for negative electrode, however, there is a problem that lithium dissolved as an ion in the electrolyte during the discharge is partly precipitated as a dendrite (dendrite crystal) in the recharge to bring about internal short-circuiting. In order to solve this problem, a technique of rendering lithium into LiAl alloy or wood alloy to weaken the activity of lithium is conducted, but this technique has a problem that sufficient performances as the secondary cell are hardly developed. And also, there is a technique of using a carbonaceous material such as graphite or the like as a material for negative electrode, which has a problem that the theoretical capacity density in the negative electrode lowers to about 1/10 as compared with that of the electrode made of metallic lithium alone. Lately, it is demanded to develop cells having high output and energy density and capable of conducting miniaturization and weight reduction with the advance of the technique for mobile phones, electric cars and the like.
Furthermore, it is recently demanded to develop compounds having fundamentally an excellent safety without the risk of ignition and the like in various fields. For example, there are studied techniques that the compound having an excellent safety without the risk of ignition or the like is included into an electrolyte in the secondary cell for backing up memories in AV-information equipments such as personal computers, VTR and the like or a power source for driving them or a paint for an aluminum can receiving the paint or a bottle of chemicals being high in the risk of ignition or the like under a high-temperature environment.
Even in the compounds having the excellent safety without the risk of ignition or the like, however, there are problems that they have a somewhat risk of ignition and are insufficient in the safety and halogen gas harmful in the environment such as chlorine gas, bromine gas or the like is generated. With the advance of the recent techniques, it is demanded to develop a method wherein various kinds of the compounds having a more excellent safety can be produced safely, cheaply and easily.